1. Field of the Invention
The invention is generally directed to pipeline sphere assemblies and, more specifically, to a seamless pipeline sphere assembly for use in a pipeline system, particularly for a meter-proving system, for product separation, or for line evacuation.
2. Description of Related Art
Pipeline spheres are commonly used in the pipeline industry for both meter proving and for product separation as well as for line evacuation, among other things. Meter proving is an activity connected with the sale of liquid product delivered through a pipeline. Pipeline meters are not entirely accurate. As such, a meter proving system is needed to measure the flow of a known volume of liquid product over a known distance in order to determine a correction factor by which the measurement must be adjusted. While different types of systems are known, a meter proving system generally comprises a length of pipeline, two detection switches, a sphere, and a launcher. The sphere is launched into the pipeline section and strikes the detection switches. A counter begins counting pulses from the meter when the first switch is activated and stops when the second switch is activated. By comparing the pulses from the meter with the known volume of the meter prover a correction factor can be determined. It is necessary to prove meters by repeating this test within a limited number of series and obtaining the same or similar measurement.
In order to properly function as a meter proving sphere, the sphere must be able to maintain its spherical shape as well as its integrity in both turbulent and non-turbulent pipelines. The sphere should also be sizable to the particular size of the pipeline in order to properly seal.
The use of pipeline spheres in product separation entails placing a sphere into the pipeline between two separate products. It is necessary that the sphere retain its spherical shape and integrity as well as be sized properly to fit the pipeline such that the products are adequately separated.
The use of pipeline spheres in line evacuation is typically employed when a line is shut down. The pipeline sphere is placed in the pipeline and pushed through the pipeline by nitrogen which is pumped behind the pipeline sphere. This action pushes any remaining product into a tank and out of the pipeline.
Traditionally, pipeline spheres have been constructed using two separate pieces, or halves, of a sphere. The sphere halves are traditionally molded separately and then bonded together. Unfortunately, the seam between the two sphere halves creates a line of weakness. This seam encourages the sphere to warp into an egg-shape (i.e. to go out of round). When a pipeline sphere goes out of round, it can no longer function properly within a pipeline. The pressure inside the sphere may also leak out and the sphere will no longer seal in the pipeline. Additionally, because of the warped shape, the sphere may become lodged within the pipeline. In meter proving systems, an out of round sphere will not launch properly and also hampers the repeatability necessary for meter proving. The warping of the sphere additionally causes the seam to fail, again resulting in a pipeline sphere that is no longer functional. Pipeline spheres are costly to change or replace. Additionally, if a sphere ruptures, it may damage the pipeline or the product contained in the pipeline.
Because of turbulence encountered inside pipelines, it is sometimes desirable to have a weighted pipeline sphere in order to stabilize the sphere within the pipeline. Non-weighted spheres are too buoyant for turbulent pipelines. Although it is known to weigh down pipeline spheres, such weight has been added by pouring lead shot into a cavity within the sphere. Unfortunately, when the sphere cracks or the seam fails, the lead shot pours into the prover which can damage the prover coating and damage the meter, pump and other measurement equipment.